1. Field of the invention:
This invention relates to a compact and lightweight copying machine comprising the body of said copying machine and a process unit attachable to and detachable from the body of the said copying machine.
2. Description of the prior art:
In recent years, electrophotographic copying machines have been developed that are constructed such that the photosensitive drum, the developing apparatus, etc., which deteriorate because of use, or which are abraded during use, are integrated together and can be readily detached from and attached to the body of the copying machine, so that the replacement of abraded parts, etc., and/or the exchange of a process unit containing black toner therein for that containing color toner therein are easy. For example, U.S. Pat. No. 4,538,896 discloses a process unit in which a photosensitive drum, a charging device, a developing device, and a cleaning apparatus are united into one body. In the said process unit, the transcription apparatus is not incorporated; it is installed in the body of the copying machine so that the transcription apparatus installed in the body of the copying machine and the photosensitive drum housed in the unit face each other in order that the recording paper be conveyed through the space between the two. As a result, the route of conveyance of the recording paper must be at the boundary between the lower part of this unit and the body of the copying machine.
When the process unit is separated from the body of the copying machine, the photosensitive drum must be housed inside the housing of the process unit so that the surface of the photosensitive drum can be protected and/or so that the toner inside the process unit is not scattered outside, and it is necessary for the housing to be closed. For this reason, the process unit disclosed in the above-mentioned U.S. Pat. No. 4,538,896 is provided with a special drum cover to cover the photosensitive drum. With such a cover, when the process unit is installed into the body of the copying machine, a part of the housing is left open, the surface of the photosensitive drum is exposed to the outside of the housing, and the transcription apparatus provided in the body of the copying machine is placed in opposition to the said photosensitive drum. In the opposite situation, when the process unit is separated from the body of the copying machine, this cover covers the surface of the photosensitive drum, so that the housing is closed. With such a drum cover, a complex mechanism is required so that a part of the housing can be opened and closed in a narrow space. Moreover, since the structure is such that a part of the housing can be opened readily, there is the danger that the user of the copying machine may accidentally touch the surface of the photosensitive drum when such a cover is used. There is also the danger that toner will be scattered around the surroundings, since the housing is made with one part left open when the drum cover is to be used.
In addition to the above, the housing of the process unit is of a complex shape since the route of conveyance of the recording paper is to be through the space between the photosensitive drum provided inside the housing of the process unit and the transcription apparatus provided in the body of the copying machine, so working with it is inconvenient.